fix(scheduled): clear stale send-now error when a row is edited

handleEdit already clears cancelErrors for the old row; also clear sendErrors
so a prior failed "Send now" doesn't leave a stale inline error after editing.
Cosmetic hygiene, matching the existing cancelErrors handling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/ScheduledMessagesTray.tsx

@@ -175,6 +175,12 @@ export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
         next.delete(oldMsg.delayId);
         return next;
       });
+      setSendErrors((prev) => {
+        if (!prev.has(oldMsg.delayId)) return prev;
+        const next = new Set(prev);
+        next.delete(oldMsg.delayId);
+        return next;
+      });
       setEditing(null);
       cancelScheduledMessage(mx, oldMsg.delayId)
         .then(() => {